NK.sub.1 receptors, NK.sub.2 receptors and NK.sub.3 receptors are known to act as tachykinin receptors. With respect to tachykinin antagonists, compounds that demonstrate selective antagonistic activity on one of NK.sub.1, NK.sub.2 and NK.sub.3 receptors, and compounds that demonstrate antagonistic activity on more than one of the sub-types of receptors (e.g. Against both NK.sub.1) and NK.sub.2 receptors) have been found in recent years. In the case of intending to inhibit comprehensively the action of tachykinin, it is important to use a compound that demonstrates antagonistic action against more than one of the types of receptors.
However, since it is generally predicted that the frequency of occurrence of effects other than the desired pharmacological effect increases when inhibiting the action of more than one of the types of receptors, a compound which demonstrate selective and potent antagonistic action against a specific receptor is also important.
Compounds considered to be structurally similar to the compounds of the present invention are disclosed in EP-776893, but these compounds demonstrate antagonistic action against both NK.sub.1, and NK.sub.2 receptors and, therefore, they should be considered to be completely different from the compounds of the present invention that selectively demonstrate antagonistic action against NK.sub.2 receptors.
With respect to selective antagonistic action against NK.sub.2 receptors, clinical studies on SR48968 (a compound having structural formula A shown below) have begun at present. Moreover, SR144190 (a compound having structural formula B shown below) is reported to have NK.sub.2 receptor-selective antagonistic activity that is more potent than that of SR.48968 (X. Edmonds-Salt. Et al., Tachykinin in Health and Disease, Sep. 7-11, 1997 in Cairns, Australia, Abstract p. 5). ##STR2##